GGPLOT Histogram with Density Curve in R using Secondary Y-axis

Prerequisites

Load the required R packages:

library(ggpubr)
library(cowplot)

Data preparation

set.seed(1234)
wdata = data.frame(
  sex = factor(rep(c("F", "M"), each=200)),
  weight = c(rnorm(200, 55), rnorm(200, 58)))
head(wdata)

##   sex weight
## 1   F   53.8
## 2   F   55.3
## 3   F   56.1
## 4   F   52.7
## 5   F   55.4
## 6   F   55.5

Create histogram with density distribution on the same y axis

# Basic histogram without the density curve
gghistogram(
  wdata, x = "weight", 
  add = "mean", rug = TRUE,
  fill = "sex", palette = c("#00AFBB", "#E7B800")
  )

# Add the density curve on the same axis
gghistogram(
  wdata, x = "weight", y = "..density..",
  add = "mean", rug = TRUE,
  fill = "sex", palette = c("#00AFBB", "#E7B800"),
  add_density = TRUE
  )

Using a secondary y-axis for the density distribution

# 1. Create the histogram plot
phist <- gghistogram(
  wdata, x = "weight", 
  add = "mean", rug = TRUE,
  fill = "sex", palette = c("#00AFBB", "#E7B800")
)

# 2. Create the density plot with y-axis on the right
# Remove x axis elements
pdensity <- ggdensity(
  wdata, x = "weight", 
  color= "sex", palette = c("#00AFBB", "#E7B800"),
  alpha = 0
) +
  scale_y_continuous(expand = expansion(mult = c(0, 0.05)), position = "right")  +
  theme_half_open(11, rel_small = 1) +
  rremove("x.axis")+
  rremove("xlab") +
  rremove("x.text") +
  rremove("x.ticks") +
  rremove("legend")

# 3. Align the two plots and then overlay them.
aligned_plots <- align_plots(phist, pdensity, align="hv", axis="tblr")
ggdraw(aligned_plots[[1]]) + draw_plot(aligned_plots[[2]])

Conclusion

This article describes how to create a ggplot histogram with density curve in R using a secondary y-axis